(1) Field of the Invention
The present invention relates to a propelling clutch apparatus for a working vehicle, and more particularly to a technique of suppressing shocks accompanying an operation of a friction type hydraulic clutch.
(2) Description of the Prior Art
A technique of suppressing shocks accompanying an operation of a hydraulic clutch in a working vehicle is disclosed in Japanese Patent Publication Kokai No. 62-231841, for example. In this prior art construction, the oil pressure applied to the hydraulic clutch is controlled on the basis of acceleration of a propelling line occurring when the hydraulic clutch is being engaged. Thereby the clutch is promptly engageable without producing shocks. This construction includes an acceleration sensor or the like for detecting acceleration of the vehicle. The clutch control is carried out based on feedback of a detection signal from the sensor or the like also when a change speed is effected in a half-clutch state.
According to this prior art construction, when the sensor is subjected to the influence of vehicle pitching when the vehicle runs on an uneven ground, for example, the pressure control effected in response to the signal from the sensor may result in pulsations of the oil pressure applied to the clutch, thereby producing shocks. An extended time may also be required for the clutch to reach an engaged position. Thus the prior construction has room for improvement.
When engaging a friction type hydraulic clutch, pressure oil must be supplied to the clutch rapidly from start of the oil supply till its friction disk begin to contact one another to provide a half-clutch state. After the half-clutch state is secured, it is necessary to accelerate the vehicle gradually while maintaining the half-clutch state for an appropriate time, in order not to impart shocks to the propelling line.